Aircraft receiving antennae



y 5, 1955 D. E. BRIDGES ET AL 2,712,603

AIRCRAFT RECEIVING ANTENNAE Filed May 7, 1951 19 REEF? fl 1:1: \/H F 1517 I Rm 379 2g lA/Vf/VMRS D. BRIDGES W. J. O'BRIEN By: h/Llluhnow +797 ATTORIIE United States Patent Office 2,712,603 Patented July 5, 19552,112,603 AIRCRAFT RECEIVING ANTENNAE Donald Edward Bridges and WilliamJoseph. QBrien, London, England, assignors to The Decca Record CompanyLimited, London, England, a British company This invention relates toradio receiving antennae for aircraft and more: particularly toantennae, having dimensions and effective height small compared with thewavelength of the signals to be received.

' Particularly when receiving relatively low frequency signals, if anexposed metal antenna is used considerable noise is experienced due toprecipitation static i. e., due to charged particles of rain, dust orthe like striking the antenna. A thin skin of insulation applied to anantenna gives no improvement although, as the thickness of theinsulation (or the distance between the insulation and the antenna) isincreased, the static level is decreased. The size of an insulatedantenna which would substantially eliminate static, however, is toogreat to make. such a system of practical value. These facts may beexplained in the following manner: approaches the antenna, there is atransfer of charge which is, at first, very small. As the dropletreaches a distance from the antenna approximately ten times the diameterof the droplet, the rate of transfer increases appreciably althoughstill remaining too slow to produce a component of radio frequencyenergy. However, when the droplet reaches the sparking distance, thetransfer of energy is rapidly completed so producing a radio frequencydis- Iurbance in the receiver. The sparking distance is dependent to'alarge degree on the radius of the antenna and thus the proportion ofcharge transferred by spark as distinct from slow proximity transferwill be greater for small radii antennae. An insulated wire isequivalent to an insulated series of concentric metallic ringsconcentric'with the wire. The increased diameter compared with uncoveredwire tends to reduce the spark energy. Also the capacity between thesurface of the insulation and the wire considered in combination withthe effective antenna capacity acts as a capacity divider to reduce theamplitude of the disturbance at the receiver. Covering the antenna withinsulation thus reduces precipitation static to a certain extent but asmentioned above it cannot be eliminated completely in this manner sincethe bulk of the insulation required would not be practicable. Accordingto this invention, a non-directional receiving antenna for an aircraftcomprises two adjacent conductors, one of which forms an antenna memberand is adapted to be coupled to the input of a receiver and the secondof which is so constructed and disposed in front of the antenna memberas to form a shield member which, when connectedto the ground terminalof a receiver, either directly or through an impedance. of small value,shields the antenna member electrically from chargedv particles of dust,rain or the like impinging upon the antenna system. The earthy terminalof the receiver is that connected to the main metallic structure of theaircraft. Impedance of small value is to be understood to mean animpedance small compared with that of the capacity between the shieldingconductor and the effective ground, i; e., the body of the aircraft.

By this arrangement, precipitation static may be sub- As a chargeddroplet of rain also caused by corona.

stantially reduced or eliminated. This may be explained in the followingmanner: A complete metallic screen around an antenna wire offers noadvantage over an insulated antenna having the same outside diameter butit is well known that, if such a screen were grounded, both the receivedsignal and the static will be suppressed. In an aircraft, however,practically all the droplets or particles striking an antenna or otherobject will impinge on the leading part. it thus becomes possible toprovide a grounded shield for the antenna which is effective inpreventing a charge transfer from charged rain droplets or otherparticles onto the receiving antenna without causing an undue loss inthe strength of the received signal. Provided the antenna dimensions aresmall compared with the wavelength, for example, not greater thanone-thirtieth of the wavelength, the antenna currents produce onlynegligible voltage drops in the antenna conductors compared with thereceived open circuit voltages and the system may be treated as acapacity network, the self and mutual inductances being negligible.Thus, if the screen is connected directly to the body of the aircraft,it can be. regarded as being wholly at ground potential and thescreening is completed. Also provided the antenna dimensions are smallcompared with the wavelength, the system will be non-directional andfree from phase diiferences between the received waves and the outputsignal.

In addition to precipitation static, radio interference is It is. wellknown that the static from corona discharge from an antenna may beprevented by using wick dischargers or by enclosing the antenna ininsulating material. Thus, in one arrangement according to theinvention, a non-directional receiving antenna comprises a hollowstructure of insulating material adapted to surround an uprightconducting element forming an antenna member and having a layer ofconducting mate.- rial forming a shield member on the surface of orembedded within the leading portion of the insulating structure toshield the antenna member. electrically from charged particles of dustor rain impinging on the antenna system. In this construction theinsulating material prevents static from corona discharge and mayconveniently be shaped to form a streamlined antenna system. It-will beappreciated that a covering of insulating material over the shieldingconductor does not affect its ability to shield the antenna electricallyfrom charged particles.

According to another aspect of the invention, a non- I directionalreceiving antenna for an aircraft comprises a hollow mastof insulatingmaterial formed of streamlined section, an antenna member formed by aconducting element inside said mast and a shield member of conductingmaterial disposed in front of the antenna member.

It is found that with a structure of conventional streamlined section,practically all the charged particles will strike the antenna structurein an are extending for about around the leading edge. .Thus in anarrangement in which. the hollow structure or mast is of streamlinedsection, the shield member may be arranged to extend around theleadingportion, of said hollow structure or mast for an arc ofapproximately 120. Conveniently the structure is closed at the top andthe conducting material arranged to extend around the-top part of themast.

The mast may be built of laminated insulating material in which case,the conducting material for the shield may conveniently be a sheet ofmetal disposed between two of the layers of the insulating material.

The conducting member inside the made in the form of a blade or plate.

According to a further feature of the invention, a radio mast ispreferably receiving system for an aircraft comprises a non-directennamember directly to the input terminal and means coupling the shieldmember either directly or through a small resistance to the groundterminal.

It will be appreciated that there will be some loss in the antennaoutput compared with a simple antenna of similar dimensions anddisposition because of the capacity of the antenna member to the shieldmember. This loss may be substantially reduced by providing a valveampli fier, the antenna member and the shield member being connected tothe input terminals of the amplifier which is arranged to have a lowimpedance output and to provide an output voltage of amplitude slightlyless than the input voltage and in phase therewith, and by providingmeans for applying the amplifier output signal between the shield memberand ground so as to reduce the effect of the capacity of the shieldmember to the antenna member, By ground is meant the main metallicstructure of the air craft. If the output is applied between the shieldmember and ground, the capacity loading of the antenna member caused byits capacity to the shield member is reduced in a ratio which is equalto the reciprocal of the difference of the gain from unity.

Conveniently the valve amplifier may comprise a valve arranged as acathode follower with the antenna member connected to the input grid ofthe valve and the shield member connected to the cathode of the valve.

If desired, the shield member may be used as an aerial for very highfrequencies; this may be done by connecting, in the leads from theantenna and shield members to the receiver, impedance elements havin ahigh impedance to signals of very high frequency. it will readily beappreciated that with a large difference of frequencies. it is possibleto isolate a low frequency receiver from the very high frequency signalsin this Way without affecting the reception of the desired low frequencysignals. As there is no ultra high frequency component in the rainstatic, the anti-static considerations, including the dimensionlimitations with regard to wavelength. do not apply at thesefrequencies.

The following is a description of a number of embodiments of theinvention, reference being made to the accom-- panying drawings, inwhich:

Figure l is a diagrammatic representation of part of an aircraft showingthe radio receiving system,

Figure 2 is a horizontal section through the antenna system of Figure 1along the line 22, and

Figures 3 and 4 are diagrammatic representations of part of an aircraftshowing modified forms of the radio receiving system of Figure 1.

Referring to Figure 1, there is shown, diagrammatically, part of thebody of an aircraft which is adapted to travel in the direction of thearrow 11. Carried on the upper surface of the body 10 is a hollow mast12 which is closed at the top and is of streamlined section. as is seenin Figure 2. This mast is formed of insulating material. and may. forexample, be constructed of layers of glass fibre cloth bonded togetherwith a suitable resin. Around the leading portion of the mast isarranged a conducting sheet 13, which forms the shield member and whichextends through an arc of about 120 as seen in Figure 7.. This sheet 13is shown, for clarity. as beinrr on the inner surface of the mast butwhen the latter is formed of laminated insulating material. the sheet 13is conveniently disposed between two of the layers of in sulatingmaterial. The shield member 13 may be a sheet. of metal but convenientlyis formed of metal gauze. Inside the mast is an antenna membercomprising an upright blade 14 which extends rearwardly from about therearward edge of the shield member 13.

In the arrangement illustrated in Figure l, the shield member 13 isconnected directly to ground, that is, to the main metallic structure ofthe aircraft. The antenna member 14 is connected to the grid of anamplifier valve 15, the output of which is fed to a receiver indicateddiagrammatically by the rectangle 16. With this antenna system, anycharged particles of dust, rain or the like will strike the leadingportion of the mast 12 in the region of the shield member 13, due to theforward motion of the aircraft. Since the shield member is grounded, thecharges on the particles will not be transferred to the antenna and thuswill not cause static noise in the receiver. As previously stated, thepresent invention relates to antenna systems having dimensions and aneffective height small compared with the wavelength. The antenuacurrents produce, therefore, only negligible voltage drops in theantenna conductors. The shield member 13, therefore, can be regarded asbeing wholly at ground potcntial and the screening is effective over thewhole length of the antenna. It will also be noted that the insulatingmast 12 totally encloses the antenna and thus will prevent staticinterference from corona discharge.

In the modified form of receiving system illustrated in Figure 3, theantenna member 14 is connected, as in Fig ure 1, to the grid of thevalve 15. The valve in Figure 2 is arranged as a cathode follower, thecathode being connected to ground through a bias resistance 17 and aload resistance 18. The shield member 13 is connected not to earth butto the junction of the resistors 17 and 18. The output voltage of thecathode follower developed across the resistance 18 is in phase with theinput signal, that is the signal between the antenna member 14 and theshield member 13, but is of slightly smaller amplitude. This outputsignal is applied between the shield member 13 and ground and thisreduces the effect of the capacity loading of the antenna member by itscapacity to the shield member. As previously explained, the capacityloading is reduced in a ratio which is equal to the reciprocal of thedifference of the gain from unity. The feed to the receiver 16 may betaken from the anode of the valve as before.

In Figure 4 there is illustrated a modification of the arrangement ofFigure 3 in which provision is made for utilising the shield member 13as a very high frequency antenna. For this purpose, inductances 19, 20are connected in the leads from the shield member 13 and the antennamember 14 to the input circuit of the valve 15. These inductances arearranged to present a high impedance to the very high frequency signalsbut to have a low impedance for the relatively low frequency signalssuch as are to be received by the receiver 16. These inductances 19, 20therefore isolate the input circuit of the valve 15 from the very highfrequency signals which can be fed through a condenser 21 to a very highhe quency receiver indicated by the rectangle 22. It will be appreciatedthat since there are no very high frequency components in the rainstatic, anti-static considerations do not arise so far as the very highfrequency system is concerned.

We claim:

I. A radio receiving system for an aircraft comprising two adjacentconductors one of which forms an antenna member and the second of whichis so constructed and disposed around the front of and wholly forward ofthe rear edge of the antenna member as to form a shield member, areceiver having an input terminal and a ground terminal for receiving asignal applied between said input terminal and said ground terminal,means coupling said antenna member to said input terminal and animpedance of negligible value connecting said shield member to saidground terminal.

2. A radio receiving system for an aircraft comprising a hollow mast ofinsulating material formed of stream-lined section, a conducting elementforming an antenna member inside said mast, a shield member ofconducting material disposed around the front of and wholly forward ofthe rear edge of the antenna member, a receiver having an input terminaland a ground terminal for receiving a signal applied between said inputterminal and said ground terminal, means coupling said antenna member tosaid input terminal and an impedance of negligible value connecting saidshield member to said earthy terminal.

3 A radio receiving system for an aircraft according to claim 2 whereinsaidshieldmember is embedded within the insulating material forming theleading portion of the hollow mast. I

4. A radioreceiving system for an aircraft according to claim 2 whereinsaid shield member extends around the leading portion of said hollowmast for an arc of approximately 120.

5. A non-directional radio receiving system for an aircraft comprising ahollow mast of laminated insulating material formed of stream-linedsection, a conducting element forming an antenna member inside saidmast, a shield member of conducting material disposed between two of thelayers of said insulating material and extending around the front of andwholly forward of the rear edge of said mast, a receiver having an inputterminal and a ground terminal for receiving a signal applied betweensaid input terminal and said ground terminal, means coupling saidantenna member to said input terminal and an impedance of negligiblevalue connecting said shield member to said ground terminal.

6. A non-directional radio receiving system for an aircraft comprising ahollow mast of insulating material, a shield member of conductingmaterial extending around the front part of said mast, a blade antennamember inside said mast and disposed so as to extend rearwardly fromsubstantially the rear edges of the shield member, a receiver having aninput terminal and a ground terminal for receiving a signal appliedbetween said input terminal and said ground terminal of the receiver,means coupling said antenna member to said input terminal and animpedance of negligible value connecting said shield member to saidground terminal.

7. A non-directional radio receiving system for an aircraft comprisingan upright antenna member, a conducting shield member extending aroundan arc in front of and wholly forward of the rear edge of the antennamember, a receiver having an input terminal and a ground terminal forreceiving signals applied between said input and said ground terminals,a low impedance circuit connecting the antenna member to the inputterminal and an impedance of negligible value connecting the shieldmember to the ground terminal.

8. A non-directional radio receiving system for an aircraft forreceiving signals of a given frequency comprising an upright antennamember having dimensions not exceeding one thirtieth of the wavelengthcorresponding to said given frequency, tending around an arc in front ofand wholly forward of the rear edge of the antenna member, a receiverhaving an input terminal and a ground terminal for receiving signalsapplied between said input and said ground terminals, a circuit having alow impedance at said given frequency connecting the antenna member tosaid input terminal and a circuit having a negligible impedance at saidgiven frequency connecting the shield memberto said ground terminal.

9. A non-directional radio receiving system for an aircraft comprisingan upright antenna member, a conducting shield member extending aroundan arc in front of said antenna member, said antenna member and saidshield member being insulated from the aircraft structure, a valveamplifier having a pair of input terminals and arranged to have a lowimpedance output and to provide an output voltage of amplitude slightlyless than and in phase with the input voltage across said inputterminals, low impedance circuit means connecting the antenna member andthe shield member respectively to the two input terminals and means forapplying the amplifier output signal between the shield member and theaircraft structure.

10. A non-directional radio receiving system according to claim 9wherein said valve amplifier comprises a a conducting shield memberexvalve having an input grid and a cathode and arranged as a cathodefollower with the antenna member con.- nected to the input grid and theshield member connected to the cathode.

11. A non-directional radio receiving antenna for an aircraft comprisinga hollow mast of insulating material formed of stream-lined section, aconducting element forming an antenna member inside said mast and ashield member of conducting material grounded through an impedance ofnegligible value extending around the leading portion of said mast foran arc of less than 12. A non-directional radio receiving antennaaccording to claim 11 wherein said antenna member comprises an uprightblade with its front edge to the rear of the rear edges of the shieldmember.

13. A non-directional radio receiving antenna for an aircraft comprisinga hollow mast of laminated insulating material formed of stream-linedsection, a conducting element forming an antenna member inside said mastand a shield member of conducting material disposed between two of thelayers of said insulating material and extending around the front partonly for an are less than 180 of said mast, said shield being groundedby an impedance of negligible value.

14. A radio receiving system for an aircraft comprising two adjacentupright conductors one of which forms an antenna member of length lessthan one-thirtieth of a wavelength of the signal to be received and thesecond of which is so constructed and disposed in front of the antennamember to form a shield member which shield member extends around thefront of the antenna member and has its rear edge forward of the rearedge of the antenna member by a distance not greater than the thickness,in the front of rear direction, of the antenna member, a receiver havinga pair of input terminals, and means connecting one of said terminals tosaid antenna member and the other of said terminals to said shieldmember, the impedance of said connecting means being of negligible valueat the frequency of the signals to be received.

15. In an aircraft, a non-directional radio receiving system comprisingan upright antenna conductor, a discharging surface forward of theantenna conductor, a capacity shielding conductor disposed between saidsurface and said antenna conductor such as to provide substantiallyperfect electrostatic shielding between said antenna conductor and saidsurface, which shielding conductor lies in an arc around the front ofthe antenna conductor of extent limited such that the antenna conductorto aircraft structure capacity is not reduced by a factor of greaterthan ten by the introduction of said shielding conductor, a receiverhaving a pair of input terminals and means connecting one of saidterminals to said antenna conductor and the other of said terminals tosaid shielding conductor, the impedance of the connecting means being ofnegligible value at the frequency of the signals to be received.

16. In an aircraft, a radio receiving antenna system comprising anantenna conductor, a shielding conductor, and means connecting theshielding conductor to the aircraft structure, the shielding conductorextending in an are around the front of the antenna conductor and havinga surface of sufiicient area to receive substantially all of raindroplets impinging on the antenna system, thereby providing a sparkingsurface for charged droplets, the orientation and dimensions of the twoconductors being such that the capacity from said antenna conductor tothe inner surface of said shielding conductor shall not ex ceed tentimes the capacity from said antenna conductor to the aircraft structureand shall not be less than one hundred times the capacity from saidantenna conductor to said sparking surface and said connecting meansbeing arranged to have an impedance which is less than one hundredth ofthe impedance, at the operating frequency, of the capacity between theshielding member and aircraft structure.

References Cited in the file of this patent Bouvier et a1. .June 8, 1937Carlson Sept. 17, 1940 Hefele Aug. 5, 1941 Harris Jan. 30, 1945Busignies Feb. 5, 1946 Bennett Feb. 25, 1947

